Drive motor displacement control

ABSTRACT

A power machine can include a hydraulic drive system that includes an infinitely variable hydraulic drive motor. A run-time displacement of the hydraulic motor can be adjusted based on commanded travel speed or based on a output torque. In some case, the run-time displacement can be selected from one of a plurality of displacement ranges, such as a high range and a low range.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/902,731, filed Sep. 19, 2019 and titled “Drive Motor DisplacementControl,” the entirety of which is incorporated herein by reference.

BACKGROUND

This disclosure is directed toward power machines. More particularly,this disclosure is directed toward controlling displacement of a drivemotor of a hydraulic drive system during operation of a power machine.Power machines, for the purposes of this disclosure, include any type ofmachine that generates power to accomplish a particular task or avariety of tasks. One type of power machine is a work vehicle. Workvehicles are generally self-propelled vehicles that have a work device,such as a lift arm (although some work vehicles can have other workdevices) that can be manipulated to perform a work function. Workvehicles include loaders, excavators, utility vehicles, tractors, andtrenchers, to name a few examples.

Some power machines can convert power from a power source (e.g., anengine) into a form that can be used by a hydraulic drive system to movethe machine (i.e., for traction control) or to operate work implements,such as a lift arm. For example, a hydraulic drive system can include atleast one pump driven by the power source. The pump can be configured todrive one or more motors, which in turn, rotate axles coupled totractive elements, such as wheels. During operation, however, the powerdemand from a hydraulic drive system can, in some instances, outstripthe capacity of a power source.

The discussion above is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

SUMMARY

Some embodiments disclosed herein can include systems and relatedmethods for improving operation of hydraulic drive systems bycontrolling displacement of an infinitely variable displacement drivemotor based on commanded travel speed, output torque, or other factors.

In some embodiments, a hydraulic drive system for use in a power machinecan include a hydraulic circuit and a control device. The hydrauliccircuit can include a hydraulic pump in hydraulic communication with ahydraulic motor. The hydraulic motor can be configured to operate withinfinitely variable displacement to drive the power machine. The controldevice can be configured to determine a control value based on one ormore of: a commanded travel speed for the power machine or a pressure inthe hydraulic circuit. The control device can be further configured tochange a run-time displacement of the hydraulic motor based upon thedetermined control value.

In some embodiments, a hydraulic circuit of a hydraulic drive system foruse in a power machine can include a hydraulic pump in hydrauliccommunication with a hydraulic drive motor, the hydraulic drive motorbeing configured to operate with infinitely variable displacement todrive the power machine. A control device can be configured to determinean output torque value associated with the hydraulic drive motor and toadjust a run-time displacement of the hydraulic drive motor based uponthe determined output torque value.

In some embodiments, a method is provided to control run-time operationof a drive system of a power machine. One or more signals can bereceived, the one or more signals indicating one or more of a commandedtravel speed for the power machine or an output torque associated withan infinitely variable displacement hydraulic drive motor of a hydraulicdrive circuit of the power machine. A control value can be determinedfor an infinitely variable displacement hydraulic drive motor of thehydraulic drive circuit, based on the one or more signals. A run-timedisplacement for the hydraulic drive motor can be adjusted based on thecontrol value.

This Summary and the Abstract are provided to introduce a selection ofconcepts in a simplified form that are further described below in theDetailed Description. This Summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor arethey intended to be used as an aid in determining the scope of theclaimed subject matter.

DRAWINGS

FIG. 1 is a block diagram illustrating functional systems of arepresentative power machine on which embodiments of the presentdisclosure can be advantageously practiced.

FIGS. 2-3 illustrate perspective views of a representative power machinein the form of a skid-steer loader of the type on which the disclosedembodiments can be practiced.

FIG. 4 is a block diagram illustrating components of a power system of aloader such as the loader illustrated in FIGS. 2-3.

FIG. 5 is a schematic of a power machine of the type on which thedisclosed embodiments can be practiced, with a hydrostatic drive systemthat includes a hydraulic pump in hydraulic communication with ahydraulic motor.

FIG. 6 is a graph depicting operational displacement ranges of thehydraulic motor of FIG. 5 according to some embodiments disclosedherein.

FIG. 7 is a schematic representation of a method for controllingdisplacement of a hydraulic motor according to some embodimentsdisclosed herein.

FIG. 8 is a graph depicting run-time displacement of a hydraulic pumpand a hydraulic motor of a hydraulic drive circuit during operation of apower machine according to some embodiments disclosed herein.

DETAILED DESCRIPTION

The concepts disclosed in this discussion are described and illustratedby referring to exemplary embodiments. These concepts, however, are notlimited in their application to the details of construction and thearrangement of components in the illustrative embodiments and arecapable of being practiced or being carried out in various other ways.The terminology in this document is used for the purpose of descriptionand should not be regarded as limiting. Words such as “including,”“comprising,” and “having” and variations thereof as used herein aremeant to encompass the items listed thereafter, equivalents thereof, aswell as additional items.

In some configurations, a hydraulic pump for a hydraulic drive system ofa power machine is a bi-hydrostatic drive pump that is powered by apower source and that is in hydraulic communication with a drive motorfor traction control. In some configurations, each lateral side of thepower machine can have its own drive pump and motor combination that ispowered by the power source. In other configurations, each tractiveelement can have its own dedicated drive pump and motor combination. Acontrol device, such as an electronic or electro-hydraulic controller,can be configured to receive operator inputs and control the traction ofthe power machine by varying the displacement of the hydraulic pump,and, in some instances, the drive motor.

During operation of a power machine, the power demand from a hydraulicdrive system can, in some instances, outstrip the capacity of a powersource. This can cause the power source to stall, with correspondingadverse effects on active operations. Further, in other instances, otherdeficiencies or excesses in the immediate power capacity of a powersource and an associated hydraulic drive system can cause certainpower-machine systems to operate in a less than desirable manner. Forthese and other reasons, it may be beneficial to provide power machineswith power management systems, including as it relates to operation ofhydraulic drive systems.

Various embodiments disclosed herein can address these and other needs,including by providing systems and corresponding methods to controlcontinuous displacement of a drive motor of a hydraulic drive systemduring operation of a power machine. For example, some embodiments canprovide systems (and methods) for changing a displacement of a drivemotor in response to changes in commanded travel speed for a powermachine. Similarly, some embodiments can provide systems (and methods)for changing a displacement of a drive motor in response to outputtorque for a drive system exceeding a threshold torque value, includingwhile keeping the associated power source at a substantially constantoutput. For example, for a given output of the power source and a fixeddisplacement of an associated hydraulic pump, motor displacement can bedecreased, as needed, to achieve a commanded increase in travel speed.Similarly, for a given output of the power source and a fixeddisplacement of the associated hydraulic pump, motor displacement can beincreased, as needed, to provide higher torque (in some cases, with acorresponding loss of travel speed).

In some embodiments, a drive system can include a hydrostatic or otherhydraulic drive circuit that includes a hydraulic pump in hydrauliccommunication with a hydraulic motor. The hydraulic motor can beconfigured to operate with infinitely variable displacement to drive thepower machine. A control device, such as an electronic orelectro-hydraulic controller, can be configured to control displacementof the motor based on different parameters. For example, the controldevice can be configured to determine a control value based on (e.g.,equal to) a commanded travel speed for the power machine and to reduce arun-time displacement of the hydraulic motor based upon the controlvalue.

In some embodiments, a hydraulic motor can be configured to operateselectively in a high range and in a low range, which may be selectableby an operator of the machine. Generally, the high range and the lowrange can encompass respective continuously variable ranges of motordisplacements, with the low range exhibiting a smaller span betweenmaximum and minimum displacement than the high range. This stands incontrast, for example, to conventional systems in which drive motors canbe controlled only to move discretely between high and lowfixed-displacement settings.

In some embodiments, a maximum motor displacement of a high range can bethe same as a maximum motor displacement of a low range, and a minimumdisplacement of the high range can be lower than a minimum displacementof the low range. For example, a high range and a low range for ahydraulic drive motor can both define the same maximum displacement,which corresponds to the maximum possible displacement for the motor.Further, the high range can define a minimum displacement thatcorresponds to the minimum possible displacement for the motor, and thelow range can define a minimum displacement that is larger than theminimum possible displacement for the motor. Accordingly, for example,the high and low ranges can both provide maximum possible torque fortraction and can overlap over a common continuous range of displacementvalues, but operation in the high range can allow a power machine totravel with a wider range of speeds (and torques) than the low range,including a range of faster speeds than may be possible in the lowrange.

In some embodiments, a control device can be configured to control ahydraulic motor to operate, as a default, at a maximum output torquelevel (i.e., at maximum motor displacement) and to reduce availableoutput torque (i.e., to reduce motor displacement) only as needed toincrease vehicle speed. In some embodiments, when a hydraulic motor isoperating at reduced torque (i.e., not at maximum displacement), acontrol device can be configured to determine an output torque valueassociated with the hydraulic motor (e.g., via sensed pressuremeasurements) and to increase a run-time displacement of the hydraulicmotor based upon the determined output torque value, regardless of theeffect on travel speed for the power machine. In this way, for example,the control device can help to ensure that appropriate torque isprovided for traction, even if this results in reduced travel speed forthe power machine. In some embodiments, motor displacement can beincreased only when the determined output torque value exceeds apredetermined torque threshold. Because system pressure is proportionalto torque and inversely proportional to displacement, this approach can,for example, usefully reduce system pressure for a given (e.g.,threshold) torque and thereby reduce strain on hydraulic components.

Thus, for example, embodiments of the disclosure can provide beneficialpower management for a power machine, including as may optimally balancethe sometimes-competing goals of providing necessary torque andproviding a commanded travel speed. In some embodiments, for example,within either of two (or more) displacement ranges for a drive motor andstarting from operation with maximum motor displacement andcorrespondingly maximized output torque at a traction device, thedisplacement of the hydraulic motor can be controllably decreased tomatch a commanded travel speed. Thus, maximum torque can be madeavailable as a default, but elevated commanded travel speeds can bereadily accommodated. Likewise, after reducing motor displacement toprovide an increase in travel speed, displacement can then be increased,in response to sensed increase of output torque (e.g., past a threshold)to ensure that appropriate tractive torque is available without theelevated strain that can be introduced by elevated hydraulic pressures.

These concepts can be practiced on various power machines, as will bedescribed below. A representative power machine on which the embodimentscan be practiced is illustrated in diagram form in FIG. 1 and oneexample of such a power machine is illustrated in FIGS. 2-3 anddescribed below before any embodiments are disclosed. For the sake ofbrevity, only one power machine is illustrated and discussed as being arepresentative power machine. However, as mentioned above, theembodiments below can be practiced on any of a number of power machines,including power machines of different types from the representativepower machine shown in FIGS. 2-3. Power machines, for the purposes ofthis discussion, include a frame, at least one work element, and a powersource that can provide power to the work element to accomplish a worktask. One type of power machine is a self-propelled work vehicle.Self-propelled work vehicles are a class of power machines that includea frame, work element, and a power source that can provide power to thework element. At least one of the work elements is a motive system formoving the power machine under power.

FIG. 1 is a block diagram that illustrates the basic systems of a powermachine 100, which can be any of a number of different types of powermachines, upon which the embodiments discussed below can beadvantageously incorporated. The block diagram of FIG. 1 identifiesvarious systems on power machine 100 and the relationship betweenvarious components and systems. As mentioned above, at the most basiclevel, power machines for the purposes of this discussion include aframe, a power source, and a work element. The power machine 100 has aframe 110, a power source 120, and a work element 130. Because powermachine 100 shown in FIG. 1 is a self-propelled work vehicle, it alsohas tractive elements 140, which are themselves work elements providedto move the power machine over a support surface and an operator station150 that provides an operating position for controlling the workelements of the power machine. A control system 160 is provided tointeract with the other systems to perform various work tasks at leastin part in response to control signals provided by an operator.

Certain work vehicles have work elements that can perform a dedicatedtask. For example, some work vehicles have a lift arm to which animplement such as a bucket is attached such as by a pinning arrangement.The work element, i.e., the lift arm can be manipulated to position theimplement to perform the task. The implement, in some instances can bepositioned relative to the work element, such as by rotating a bucketrelative to a lift arm, to further position the implement. Under normaloperation of such a work vehicle, the bucket is intended to be attachedand under use. Such work vehicles may be able to accept other implementsby disassembling the implement/work element combination and reassemblinganother implement in place of the original bucket. Other work vehicles,however, are intended to be used with a wide variety of implements andhave an implement interface such as implement interface 170 shown inFIG. 1. At its most basic, implement interface 170 is a connectionmechanism between the frame 110 or a work element 130 and an implement,which can be as simple as a connection point for attaching an implementdirectly to the frame 110 or a work element 130 or more complex, asdiscussed below.

On some power machines, implement interface 170 can include an implementcarrier, which is a physical structure movably attached to a workelement. The implement carrier has engagement features and lockingfeatures to accept and secure any of a number of different implements tothe work element. One characteristic of such an implement carrier isthat once an implement is attached to it, it is fixed to the implementnot movable with respect to the implement) and when the implementcarrier is moved with respect to the work element, the implement moveswith the implement carrier. The term implement carrier as used herein isnot merely a pivotal connection point, but rather a dedicated devicespecifically intended to accept and be secured to various differentimplements. The implement carrier itself is mountable to a work element130 such as a lift arm or the frame 110. Implement interface 170 canalso include one or more power sources for providing power to one ormore work elements on an implement. Some power machines can have aplurality of work element with implement interfaces, each of which may,but need not, have an implement carrier for receiving implements. Someother power machines can have a work element with a plurality ofimplement interfaces so that a single work element can accept aplurality of implements simultaneously. Each of these implementinterfaces can, but need not, have an implement carrier.

Frame 110 includes a physical structure that can support various othercomponents that are attached thereto or positioned thereon. The frame110 can include any number of individual components. Some power machineshave frames that are rigid. That is, no part of the frame is movablewith respect to another part of the frame. Other power machines have atleast one portion that can move with respect to another portion of theframe. For example, excavators can have an upper frame portion thatrotates with respect to a lower frame portion. Other work vehicles havearticulated frames such that one portion of the frame pivots withrespect to another portion for accomplishing steering functions.

Frame 110 supports the power source 120, which is configured to providepower to one or more work elements 130 including the one or moretractive elements 140, as well as, in some instances, providing powerfor use by an attached implement via implement interface 170. Power fromthe power source 120 can be provided directly to any of the workelements 130, tractive elements 140, and implement interfaces 170.Alternatively, power from the power source 120 can be provided to acontrol system 160, which in turn selectively provides power to theelements that capable of using it to perform a work function. Powersources for power machines typically include an engine such as aninternal combustion engine and a power conversion system such as amechanical transmission or a hydraulic system that is configured toconvert the output from an engine into a form of power that is usable bya work element. Other types of power sources can be incorporated intopower machines, including electrical sources or a combination of powersources, known generally as hybrid power sources.

FIG. 1 shows a single work element designated as work element 130, butvarious power machines can have any number of work elements. Workelements are typically attached to the frame of the power machine andmovable with respect to the frame when performing a work task. Inaddition, tractive elements 140 are a special case of work element inthat their work function is generally to move the power machine 100 overa support surface. Tractive elements 140 are shown separate from thework element 130 because many power machines have additional workelements besides tractive elements, although that is not always thecase. Power machines can have any number of tractive elements, some orall of which can receive power from the power source 120 to propel thepower machine 100. Tractive elements can be, for example, trackassemblies, wheels attached to an axle, and the like. Tractive elementscan be mounted to the frame such that movement of the tractive elementis limited to rotation about an axle (so that steering is accomplishedby a skidding action) or, alternatively, pivotally mounted to the frameto accomplish steering by pivoting the tractive element with respect tothe frame.

Power machine 100 includes an operator station 150 that includes anoperating position from which an operator can control operation of thepower machine. In some power machines, the operator station 150 isdefined by an enclosed or partially enclosed cab. Some power machines onwhich the disclosed embodiments may be practiced may not have a cab oran operator compartment of the type described above. For example, a walkbehind loader may not have a cab or an operator compartment, but ratheran operating position that serves as an operator station from which thepower machine is properly operated. More broadly, power machines otherthan work vehicles may have operator stations that are not necessarilysimilar to the operating positions and operator compartments referencedabove. Further, some power machines such as power machine 100 andothers, whether or not they have operator compartments or operatorpositions, may be capable of being operated remotely (i.e. from aremotely located operator station) instead of or in addition to anoperator station adjacent or on the power machine. This can includeapplications where at least some of the operator-controlled functions ofthe power machine can be operated from an operating position associatedwith an implement that is coupled to the power machine. Alternatively,with some power machines, a remote-control device can be provided (i.e.remote from both of the power machine and any implement to which is itcoupled) that is capable of controlling at least some of theoperator-controlled functions on the power machine.

FIGS. 2-3 illustrate a loader 200, which is one particular example of apower machine of the type illustrated in FIG. 1 where the embodimentsdiscussed below can be advantageously employed. Loader 200 is askid-steer loader, which is a loader that has tractive elements (in thiscase, four wheels) that are mounted to the frame of the loader via rigidaxles. Here the phrase “rigid axles” refers to the fact that theskid-steer loader 200 does not have any tractive elements that can berotated or steered to help the loader accomplish a turn. Instead, askid-steer loader has a drive system that independently powers one ormore tractive elements on each side of the loader so that by providingdiffering tractive signals to each side, the machine will tend to skidover a support surface. These varying signals can even include poweringtractive element(s) on one side of the loader to move the loader in aforward direction and powering tractive element(s) on another side ofthe loader to mode the loader in a reverse direction so that the loaderwill turn about a radius centered within the footprint of the loaderitself. The term “skid-steer” has traditionally referred to loaders thathave skid steering as described above with wheels as tractive elements.However, it should be noted that many track loaders also accomplishturns via skidding and are technically skid-steer loaders, even thoughthey do not have wheels. For the purposes of this discussion, unlessnoted otherwise, the term skid-steer should not be seen as limiting thescope of the discussion to those loaders with wheels as tractiveelements.

Loader 200 is one particular example of the power machine 100illustrated broadly in FIG. 1 and discussed above. To that end, featuresof loader 200 described below include reference numbers that aregenerally similar to those used in FIG. 1. For example, loader 200 isdescribed as having a frame 210, just as power machine 100 has a frame110. Skid-steer loader 200 is described herein to provide a referencefor understanding one environment on which the embodiments describedbelow related to track assemblies and mounting elements for mounting thetrack assemblies to a power machine may be practiced. The loader 200should not be considered limiting especially as to the description offeatures that loader 200 may have described herein that are notessential to the disclosed embodiments and thus may or may not beincluded in power machines other than loader 200 upon which theembodiments disclosed below may be advantageously practiced. Unlessspecifically noted otherwise, embodiments disclosed below can bepracticed on a variety of power machines, with the loader 200 being onlyone of those power machines. For example, some or all of the conceptsdiscussed below can be practiced on many other types of work vehiclessuch as various other loaders, excavators, trenchers, and dozers, toname but a few examples.

Loader 200 includes frame 210 that supports a power system 220, thepower system being capable of generating or otherwise providing powerfor operating various functions on the power machine. Power system 220is shown in block diagram form but is located within the frame 210.Frame 210 also supports a work element in the form of a lift armassembly 230 that is powered by the power system 220 and that canperform various work tasks. As loader 200 is a work vehicle, frame 210also supports a traction system 240, which is also powered by powersystem 220 and can propel the power machine over a support surface. Thelift arm assembly 230 in turn supports an implement interface 270, whichincludes an implement carrier 272 that can receive and secure variousimplements to the loader 200 for performing various work tasks and powercouplers 274, to which an implement can be coupled for selectivelyproviding power to an implement that might be connected to the loader.Power couplers 274 can provide sources of hydraulic or electric power orboth. The loader 200 includes a cab 250 that defines an operator station255 from which an operator can manipulate various control devices 260 tocause the power machine to perform various work functions. Cab 250 canbe pivoted back about an axis that extends through mounts 254 to provideaccess to power system components as needed for maintenance and repair.

The operator station 255 includes an operator seat 258 and a pluralityof operation input devices, including control levers 260 that anoperator can manipulate to control various machine functions. Operatorinput devices can include buttons, switches, levers, sliders, pedals andthe like that can be stand-alone devices such as hand operated levers orfoot pedals or incorporated into hand grips or display panels, includingprogrammable input devices. Actuation of operator input devices cangenerate signals in the form of electrical signals, hydraulic signals,and/or mechanical signals. Signals generated in response to operatorinput devices are provided to various components on the power machinefor controlling various functions on the power machine. Among thefunctions that are controlled via operator input devices on powermachine 100 include control of the tractive elements 219, the lift armassembly 230, the implement carrier 272, and providing signals to anyimplement that may be operably coupled to the implement.

Loaders can include human-machine interfaces including display devicesthat are provided in the cab 250 to give indications of informationrelatable to the operation of the power machines in a form that can besensed by an operator, such as, for example audible and/or visualindications. Audible indications can be made in the form of buzzers,bells, and the like or via verbal communication. Visual indications canbe made in the form of graphs, lights, icons, gauges, alphanumericcharacters, and the like. Displays can be dedicated to providingdedicated indications, such as warning lights or gauges, or dynamic toprovide programmable information, including programmable display devicessuch as monitors of various sizes and capabilities. Display devices canprovide diagnostic information, troubleshooting information,instructional information, and various other types of information thatassists an operator with operation of the power machine or an implementcoupled to the power machine. Other information that may be useful foran operator can also be provided. Other power machines, such walk behindloaders may not have a cab nor an operator compartment, nor a seat. Theoperator position on such loaders is generally defined relative to aposition where an operator is best suited to manipulate operator inputdevices.

Various power machines that can include and/or interacting with theembodiments discussed below can have various different frame componentsthat support various work elements. The elements of frame 210 discussedherein are provided for illustrative purposes and frame 210 is not theonly type of frame that a power machine on which the embodiments can bepracticed can employ. Frame 210 of loader 200 includes an undercarriageor lower portion 211 of the frame and a mainframe or upper portion 212of the frame that is supported by the undercarriage. The mainframe 212of loader 200, in some embodiments is attached to the undercarriage 211such as with fasteners or by welding the undercarriage to the mainframe.Alternatively, the mainframe and undercarriage can be integrally formed.Mainframe 212 includes a pair of upright portions 214A and 214B locatedon either side and toward the rear of the mainframe that support liftarm assembly 230 and to which the lift arm assembly 230 is pivotallyattached. The lift arm assembly 230 is illustratively pinned to each ofthe upright portions 214A and 214B. The combination of mounting featureson the upright portions 214A and 214B and the lift arm assembly 230 andmounting hardware (including pins used to pin the lift arm assembly tothe mainframe 212) are collectively referred to as joints 216A and 216B(one is located on each of the upright portions 214) for the purposes ofthis discussion. Joints 216A and 216B are aligned along an axis 218 sothat the lift arm assembly is capable of pivoting, as discussed below,with respect to the frame 210 about axis 218. Other power machines maynot include upright portions on either side of the frame or may not havea lift arm assembly that is mountable to upright portions on either sideand toward the rear of the frame. For example, some power machines mayhave a single arm, mounted to a single side of the power machine or to afront or rear end of the power machine. Other machines can have aplurality of work elements, including a plurality of lift arms, each ofwhich is mounted to the machine in its own configuration. Frame 210 alsosupports a pair of tractive elements in the form of wheels 219A-D oneither side of the loader 200.

The lift arm assembly 230 shown in FIGS. 2-3 is one example of manydifferent types of lift arm assemblies that can be attached to a powermachine such as loader 200 or other power machines on which embodimentsof the present discussion can be practiced. The lift arm assembly 230 iswhat is known as a vertical lift arm, meaning that the lift arm assembly230 is moveable (i.e. the lift arm assembly can be raised and lowered)under control of the loader 200 with respect to the frame 210 along alift path 237 that forms a generally vertical path. Other lift armassemblies can have different geometries and can be coupled to the frameof a loader in various ways to provide lift paths that differ from theradial path of lift arm assembly 230. For example, some lift paths onother loaders provide a radial lift path. Other lift arm assemblies canhave an extendable or telescoping portion. Other power machines can havea plurality of lift arm assemblies attached to their frames, with eachlift arm assembly being independent of the other(s). Unless specificallystated otherwise, none of the inventive concepts set forth in thisdiscussion are limited by the type or number of lift arm assemblies thatare coupled to a particular power machine.

The lift arm assembly 230 has a pair of lift arms 234 that are disposedon opposing sides of the frame 210. A first end of each of the lift arms234 is pivotally coupled to the power machine at joints 216 and a secondend 232B of each of the lift arms is positioned forward of the frame 210when in a lowered position as shown in FIG. 2. Joints 216 are locatedtoward a rear of the loader 200 so that the lift arms extend along thesides of the frame 210. The lift path 237 is defined by the path oftravel of the second end 232B of the lift arms 234 as the lift armassembly 230 is moved between a minimum and maximum height.

Each of the lift arms 234 has a first portion 234A of each lift arm 234is pivotally coupled to the frame 210 at one of the joints 216 and thesecond portion 234B extends from its connection to the first portion234A to the second end 232B of the lift arm assembly 230. The lift arms234 are each coupled to a cross member 236 that is attached to the firstportions 234A. Cross member 236 provides increased structural stabilityto the lift arm assembly 230. A pair of actuators 238, which on loader200 are hydraulic cylinders configured to receive pressurized fluid frompower system 220, are pivotally coupled to both the frame 210 and thelift arms 234 at pivotable joints 238A and 238B, respectively, on eitherside of the loader 200. The actuators 238 are sometimes referred toindividually and collectively as lift cylinders. Actuation (i.e.,extension and retraction) of the actuators 238 cause the lift armassembly 230 to pivot about joints 216 and thereby be raised and loweredalong a fixed path illustrated by arrow 237. Each of a pair of controllinks 217 are pivotally mounted to the frame 210 and one of the liftarms 232 on either side of the frame 210. The control links 217 help todefine the fixed lift path of the lift arm assembly 230.

Some lift arms, most notably lift arms on excavators but also possibleon loaders, may have portions that are controllable to pivot withrespect to another segment instead of moving in concert (i.e. along apre-determined path) as is the case in the lift arm assembly 230 shownin FIG. 2. Some power machines have lift arm assemblies with a singlelift arm, such as is known in excavators or even some loaders and otherpower machines. Other power machines can have a plurality of lift armassemblies, each being independent of the other(s).

An implement interface 270 is provided proximal to a second end 232B ofthe lift arm assembly 234. The implement interface 270 includes animplement carrier 272 that is capable of accepting and securing avariety of different implements to the lift arm 230. Such implementshave a complementary machine interface that is configured to be engagedwith the implement carrier 272. The implement carrier 272 is pivotallymounted at the second end 232B of the arm 234. Implement carrieractuators 235 are operably coupled the lift arm assembly 230 and theimplement carrier 272 and are operable to rotate the implement carrierwith respect to the lift arm assembly. Implement carrier actuators 235are illustratively hydraulic cylinders and often known as tiltcylinders.

By having an implement carrier capable of being attached to a pluralityof different implements, changing from one implement to another can beaccomplished with relative ease. For example, machines with implementcarriers can provide an actuator between the implement carrier and thelift arm assembly, so that removing or attaching an implement does notinvolve removing or attaching an actuator from the implement or removingor attaching the implement from the lift arm assembly. The implementcarrier 272 provides a mounting structure for easily attaching animplement to the lift arm (or other portion of a power machine) that alift arm assembly without an implement carrier does not have.

Some power machines can have implements or implement like devicesattached to it such as by being pinned to a lift arm with a tiltactuator also coupled directly to the implement or implement typestructure. A common example of such an implement that is rotatablypinned to a lift arm is a bucket, with one or more tilt cylinders beingattached to a bracket that is fixed directly onto the bucket such as bywelding or with fasteners. Such a power machine does not have animplement carrier, but rather has a direct connection between a lift armand an implement.

The implement interface 270 also includes an implement power source 274available for connection to an implement on the lift arm assembly 230.The implement power source 274 includes pressurized hydraulic fluid portto which an implement can be removably coupled. The pressurizedhydraulic fluid port selectively provides pressurized hydraulic fluidfor powering one or more functions or actuators on an implement. Theimplement power source can also include an electrical power source forpowering electrical actuators and/or an electronic controller on animplement. The implement power source 274 also exemplarily includeselectrical conduits that are in communication with a data bus on theexcavator 200 to allow communication between a controller on animplement and electronic devices on the loader 200.

Frame 210 supports and generally encloses the power system 220 so thatthe various components of the power system 220 are not visible in FIGS.2-3. FIG. 4 includes, among other things, a diagram of variouscomponents of the power system 220. Power system 220 includes one ormore power sources 222 that are capable of generating and/or storingpower for use on various machine functions. On power machine 200, thepower system 220 includes an internal combustion engine. Other powermachines can include electric generators, rechargeable batteries,various other power sources or any combination of power sources that canprovide power for given power machine components. The power system 220also includes a hydraulic drive system 246 integrated with a powerconversion system 224, which is operably coupled to the power source222. Power conversion system 224 is, in turn, coupled to one or moreactuators 226, which can perform a function on the power machine. Powerconversion systems in various power machines can include variouscomponents, including mechanical transmissions, hydraulic systems, andthe like. The power conversion system 224 of power machine 200 includesa pair of hydrostatic drive pumps 224A and 224B, which form part of thehydraulic drive system 246 and are selectively controllable to provide apower signal to drive motors 226A and 226B. The drive motors 226A and226B in turn are each operably coupled to axles, with drive motor 226Abeing coupled to axles 228A and 228B and drive motor 226B being coupledto axles 228C and 228D. The axles 228A-D are in turn coupled to tractiveelements 219A-D, respectively. The drive pumps 224A and 224B can bemechanically, hydraulic, and/or electrically coupled to operator inputdevices to receive actuation signals for controlling the drive pumps.

The arrangement of drive pumps, motors, and axles in power machine 200is but one example of an arrangement of these components. As discussedabove, power machine 200 is a skid-steer loader and thus tractiveelements on each side of the power machine are controlled together viathe output of a single hydraulic pump, either through a single drivemotor as in power machine 200 or with individual drive motors. Variousother configurations and combinations of hydraulic drive pumps andmotors can be employed as may be advantageous.

The power conversion system 224 of power machine 200 also includes ahydraulic implement pump 224C, which is also operably coupled to thepower source 222. The hydraulic implement pump 224C is operably coupledto work actuator circuit 238C. Work actuator circuit 238C includes liftcylinders 238 and tilt cylinders 235 as well as control logic to controlactuation thereof. The control logic selectively allows, in response tooperator inputs, for actuation of the lift cylinders and/or tiltcylinders. In some machines, the work actuator circuit also includescontrol logic to selectively provide a pressurized hydraulic fluid to anattached implement. The control logic of power machine 200 includes anopen center, 3 spool valve in a series arrangement. The spools arearranged to give priority to the lift cylinders, then the tiltcylinders, and then pressurized fluid to an attached implement.

The description of power machine 100 and loader 200 above is providedfor illustrative purposes, to provide illustrative environments on whichthe embodiments discussed below can be practiced. While the embodimentsdiscussed can be practiced on a power machine such as is generallydescribed by the power machine 100 shown in the block diagram of FIG. 1and more particularly on a loader such as track loader 200, unlessotherwise noted or recited, the concepts discussed below are notintended to be limited in their application to the environmentsspecifically described above.

FIG. 5 illustrates aspects of a hydraulic drive system that can be usedfor traction control of a power machine, including as a configurationfor the hydraulic drive system 246 of the power machine 200 of FIGS. 2and 3. In the illustrated embodiment, the hydraulic drive systemincludes a hydrostatic hydraulic drive circuit 346 that includes avariable displacement hydraulic pump 324 in hydraulic communication withan infinitely variable displacement hydraulic drive motor 326, exampledetails of which are further discussed below. In other embodiments,other types of hydraulic drive systems can be used, consistent with thegeneral principles disclosed herein.

In the illustrated embodiment, a control device 340 is operably coupledwith the hydraulic pump 324, the hydraulic motor 326, and a power source322 (e.g., an engine) that is configured to power the hydraulic pump324. In some implementations, the control device 340 can be configuredto determine a control value based on a commanded travel speed for thepower machine. The control device 340 can then adjust (e.g., reduce) arun-time displacement of the hydraulic motor 326, as needed, based uponthe determined control value. Accordingly, for example, hydraulic motor326 can be controlled to provide appropriate travel speed, withreduction of torque output only as needed.

In some embodiments, a control device the device 340) can be configuredto decrease displacement of a hydraulic motor in response to a commandedtravel speed exceeding a threshold speed. Motor speed is inverselyproportional to torque and to displacement, and torque is proportionalto displacement. Correspondingly, for example, this approach canusefully reduce torque only as may be needed to provide a particularlyhigh travel speed. In this regard, in some implementations, a speedthreshold may correspond to speeds for travel between work sites (e.g.,road speeds) rather than to speeds for transport of loads or otheroperations within a work site.

In some implementations, the control device 340 can additionally oralternatively be configured to determine an output torque valueassociated with the hydraulic motor 326. The control device 340 can thenadjust (e.g., increase) a run-time displacement of the hydraulic motor326, as needed, based upon the determined output torque value, andthereby ensure that appropriate torque is available for traction.Further, in some implementations, the control device 340 can increaserun-time displacement of the hydraulic motor 326, including to provideincreased tractive torque, regardless of the effect of such an increaseon travel speed for the power machine 100.

In different embodiments, different configurations are possible. Asillustrated in FIG. 5, for example, the hydrostatic hydraulic circuit346 includes at least one variable displacement hydraulic pump (i.e.,the pump 324) that is mechanically coupled to the power source 322,which may be similar to the power source 222 described with reference toFIG. 4. The variable displacement hydraulic pump 324 is equipped with aswash plate (not shown) that can be controlled by the control device 340to be continuously adjusted to any number of angular orientations, eachcorresponding to a corresponding displacement volume for the hydraulicpump 324. In addition, the swash plate may be a bi-directional swashplate such that adjustment may adjust the displacement of the hydraulicmotor 326 to provide for forward or reversed flow. (As used herein, theterm “bi-directional” is used to refer to a hydraulic pump or ahydraulic motor that is capable of moving fluid, such as hydraulicfluid, in either of two directions.) As such, the angle of the swashplate may vary between first, or positive, displacement orientations,such as for forward travel of the machine 100, and second, or negative,displacement orientations, such as for reverse travel of the machine100. In other embodiments, however, a drive pump can be otherwiseconfigured, including for control using different control structures.For example, a drive pump can be limited to unidirectional operation onhydraulic (as opposed to hydrostatic) drive systems and direction oftravel can be accomplished by using control valves that are external tothe drive pump to port pressurized fluid to cause tractive elements torotate in a forward or reverse direction.

Also as illustrated in FIG. 5, for example, the infinitely variabledisplacement hydraulic pump 324 is fluidly coupled to the variabledisplacement hydraulic motor 326. The hydraulic motor 326 is alsoequipped with a swash plate (not shown) that can be controlled by thecontrol device 340 to be continuously adjusted an infinite number ofangular orientations, each corresponding to a corresponding displacementvolume for the hydraulic motor 326. As similarly noted for the drivepump 324, other embodiments may include drive motors that can beotherwise configured, including for control using different controlstructures.

Thus, in the illustrated embodiment, the fluid coupling of the hydraulicmotor 326 to the infinitely variable displacement hydraulic pump 324 viafluid lines 348 a, 348 b allows the hydraulic pump 324, as powered bythe power source 322, to drive rotation of the hydraulic motor 326 andthereby power travel of the power machine over terrain. Further, theswash plate angle of the hydraulic pump 324 can be varied to determinethe direction and flow rate of the hydraulic fluid that is pumped to thehydraulic motor 326, and the swash plate angle of the hydraulic motor326 can be continuously varied to between minimum and maximumdisplacements to adjust an output torque T that is delivered to theassociated tractive element(s) (not shown).

To determine relevant parameters and control operation of the hydraulicdrive circuit 356, a controller such as the control device 340 mayinclude various known electrical, hydraulic, and other modules,including electro-hydraulic actuators, special or general purposecomputing devices, and so on. In this regard, for example, the controldevice 340 may include a processor, a memory, and an input/outputcircuit that facilitates communication to other modules that areinternal and external to the control device 340. The processor maycontrol operation of the control device 340 by executing operatinginstructions, such as, for example, computer readable program codestored in memory, wherein operations may be initiated internally orexternally to the control device 340. The memory may comprise temporarystorage areas, such as, for example, cache, virtual memory, or randomaccess memory, or permanent storage areas, such as, for example,read-only memory, removable drives, network/internet storage, harddrives, flash memory, memory sticks, or any other known volatile ornon-volatile data storage devices. Such devices may be locatedinternally or externally to the control device 340. Although a singlecontrol device 340 is described, it will be appreciated that some powersystems can include a different number or configuration of controldevices, including control devices that are distributed about therelevant power machine or located remotely from the power machine.

In the example embodiment provided in FIG. 5, the control device 340 maybe in electrical, hydraulic, or other communication with the hydraulicpump 324, the hydraulic motor 326, the power source 322, and theoperator interface 342 (e.g., a joystick, a touchscreen interface,etc.). Communication between each such component and the control device340 may be effected via wired, wireless, or other communication, via oneor more communication channels 350. For instance, the control device 340may send or receive hydraulic, electronic, or other signals over therelevant communication channel 350 to adjust angles of the swash plateof the hydraulic motor 326, such as by controlling proportionalsolenoids or other devices. Similarly, the control device 340 may sendor receive signals over the relevant communication channels 350 todetermine and, in some instances, control a speed of the power source322 (e.g., an RPM of an engine), to receive various operator commandsfrom the operator interface 342, and to provide various outputs to theoperator interface 342.

In some embodiments, one or more sensors may monitor the power system todetect various conditions and provide data signals to the control device340, such as may inform control of the drive circuit 346 (and the drivesystem generally) by the control device 340 during operation of a powermachine 100. For example, a power source sensor (not shown) may be usedto detect operating speed or other operating conditions of the powersource 322. Similarly, a pressure sensor (not shown) of a known type maybe disposed to detect a pressure at one or more locations on thehydraulic circuit 346, another sensor (not shown) of a known type may beconfigured to determine a travel speed of the power machine or otherrelated parameter (e.g., rotational speed of an axle 328), and so on.

Including for power-management reasons discussed above, the controldevice 340 is configured to selectively adjust the displacement of thehydraulic motor 326 during operation of the power machine. Inparticular, for example, the control device 340 can selectively adjustdisplacement of the hydraulic motor 326 in response to changes incommanded travel speed of the power machine, or in response to outputtorque T. In some cases, as further discussed below, the control device340 can selectively adjust displacement of the hydraulic motor 326 inresponse to output torque T exceeding a threshold torque value,including when this latter adjustment results in a decrease in travelspeed.

In one example, for a given output of the power source 322 and a givendisplacement of the hydraulic pump 324, the control device 340 candetermine a control value that is based on (e.g., equal to) a travelspeed that is commanded at the operator interface 342 or is measured,directly or indirectly, using one or more sensors. Based on the controlvalue, the control device 340 can then decrease hydraulic motor 326displacement over a continuous range of displacements, to the extentneeded to achieve the commanded increase in travel speed. Further, insome implementations, converse adjustments are also possible, underwhich the control device 340 can increase displacement of the hydraulicmotor 326 over a continuous range, to correspond to a decrease incommanded travel speed.

As another example, for a given output of the power source 322 and agiven displacement of the hydraulic pump 324, the control device 340 candetermine an output torque value based on (e.g., equal to) a measuredoutput torque, such as by using pressure measurements from the hydraulicdrive circuit 346 (or other data) in combination with measurementsindicative of motor displacement and a locally stored look-up table orpre-programmed set of equations. As needed, such as when the outputtorque value exceeds a threshold value, the control device 340 canincrease hydraulic motor 326 displacement over a continuous range ofdisplacements to reduce pressure. In some implementations, such anincrease in displacement for the hydraulic motor 326 can be affectedregardless of any corresponding loss of travel speed. In some cases, athreshold torque may be considered as equivalent to a threshold pressurefor a given displacement of a hydraulic machine, including such thatincreasing displacement relative a threshold torque may correspond toincreasing displacement to avoid exceeding a threshold pressure. In someembodiments, a threshold torque may vary depending on operatingconditions (e.g., based on current displacement of the hydraulic pump ormotor 324, 326, travel speed of the power machine, etc.). Further, insome embodiments, converse adjustments are also possible, under whichthe control device 340 can decrease displacement of the hydraulic motor326 over a continuous range to correspond to a decrease in outputtorque.

In some embodiments, the control device 340 can be configured, as adefault, to implement maximum displacement at the hydraulic motor 326,for a given flow within the hydraulic drive circuit 346, and thereby toprovide, as a default, maximum output torque T. For example, the controldevice 340 can be configured to implement maximum displacement at thehydraulic motor 326 as a default, then to decrease displacement at themotor 326 only as needed to match a commanded increase in travel speed.Further, after such a decrease in displacement, the control device 340can then increase motor displacement, as needed, in order to ensuresufficient output torque. For example, as also noted above, the controldevice 340 can sometimes increase motor displacement in response tosensed increase of output torque T past a threshold torque, in order toensure that appropriate output torque T is available without theelevated strain that can be introduced by elevated hydraulic pressures.

In some embodiments, as generally noted above, a control device may beconfigured to receive indications of output torque and commanded travelspeed, but to prioritize one of these factors when determining anadjustment for run-time displacement of a hydraulic motor. For example,as discussed above, the control device 340 can be configured to adjustdisplacement of the hydraulic motor 326 in response to commanded travelspeed or in response to the output torque T (e.g., as determined basedon sensed pressure). In some cases, the control device 340 may receivesignals corresponding to the commanded travel speed and to the outputtorque T, but the output torque T may be given priority over thecommanded travel speed. For example, if the output torque T isdetermined to exceed a torque threshold, a run-time displacement of thehydraulic motor 326 may be adjusted accordingly (e.g., increased, asdiscussed above), even if providing the commanded travel speed mightotherwise correspond to the control device 340 commanding a differentdecreased) run-time displacement for the hydraulic motor 326.

In some embodiments, a hydraulic motor can be controlled to operateselectively in different displacement ranges. For example, asillustrated in FIG. 6, the control device 340 can control the hydraulicmotor 326 to operate selectively with displacements in a first (e.g.,high) range 352 and displacements in a second (e.g., low) range 354.

In different implementations, the span of displacements included inhigh, low, and other displacement ranges can overlap to varying degrees.In some embodiments, including as illustrated in FIG. 6, a maximumdisplacement of the high range 352 for the hydraulic motor 326 can bethe same as a maximum displacement of the low range 354, and a minimumdisplacement of the high range 352 can be lower than a minimumdisplacement of the low range 354. In some cases, also as illustrated inFIG. 6, a high range and a low range for a hydraulic motor can bothdefine a maximum displacement that corresponds to the maximum possibledisplacement for the hydraulic motor 326. Similarly, a high range candefine a minimum displacement that corresponds to the minimum possibledisplacement for the hydraulic motor 326, and a low range can define aminimum displacement that is larger than the minimum possibledisplacement for the hydraulic motor 326. Accordingly, for example, thehigh and low ranges can both provide maximum possible output torque Tfor traction, but operation in the high range can allow a power machineto travel with a wider range of speeds (and output torques T) than thelow range.

In some embodiments, bounds of displacement ranges (e.g., the upper andlower bounds of the high and low ranges of FIG. 6) may be fixed. Forexample, the maximum and minimum displacements of one or moredisplacement ranges may be predefined and stored in the control device340. In some embodiments, the bounds of displacement ranges can beupdated during operation of the power machine. For example, the boundsof a high, low, or other displacement range can sometimes be updatedbased on various operating conditions, such as, for example, a travel orengine speed of the power machine, current states of a hydraulic drivecircuit (e.g., fluid pressure or temperature), operator demands oroperator identifiers, and so on.

In some implementations, devices or systems disclosed herein can beutilized or configured for operation using methods embodying aspects ofthe invention. Correspondingly, description herein of particularfeatures, capabilities, or intended purposes of a device or system isgenerally intended to inherently include disclosure of a method of usingsuch features for the intended purposes, a method of implementing suchcapabilities, and a method of configuring disclosed (or otherwise known)components to support these purposes or capabilities. Similarly, unlessotherwise indicated or limited, discussion herein of any method ofmanufacturing or using a particular device or system, includingconfiguring the device or system for operation, is intended toinherently include disclosure, as embodiments of the invention, of theutilized features and implemented capabilities of such device or system.

Correspondingly, some embodiments can include a method for control ofrun-time operation of a power machine that includes a hydraulic drivecircuit with a variable displacement hydraulic drive motor (e.g., theinfinitely variable displacement drive motor 326 of the power machine200, as discussed above). As one example, shown in FIG. 7, a method 400can include receiving 410, at a control device, one or more signalsindicating one or more of a commanded travel speed for the power machineor an output torque associated with an infinitely variable displacementhydraulic drive motor of a hydraulic drive circuit of the power machine.For example, an electronic or electro-hydraulic control can receiveelectrical or hydraulic signals that correspond to an operator inputthat commands a travel speed for a work machine or that correspond to atorque provided by an associated drive motor. With regard to outputtorque in particular, in some implementations, the corresponding signalsmay be provided by a pressure sensor that is configured to sensepressure for the relevant hydraulic drive circuit, with the sensedpressure corresponding to torque according to known hydraulicprinciples. In other implementations, however, other types of signalscan be received.

Still referring to FIG. 7, the method can further include, using thereceived 410 signals to determine (e.g., calculate) 420 a control valuefor the hydraulic drive motor, and adjusting 430 a run-time displacementfor the hydraulic drive motor based on the control value. In someimplementations, a determined 420 control value may be a target run-timedisplacement and a control device can then provide an appropriatesignal, using known approaches, to cause the drive motor to operate atthe target run-time displacement. In some implementations, a determined420 control value may be a value that does not directly representdisplacement, but can be used to control a drive motor to provide aparticular displacement. For example, a determined 420 control value maybe an index or other reference value for a look-up table, a gain valuefor a control signal, or other value that can be relayed, directly orindirectly, to a motor in order to controllably adjust run-timedisplacement.

As also discussed above, adjusting 430 a run-time displacement of adrive motor can sometimes correspond to a reduced travel speed of thepower machine relative to the commanded travel speed. For example, insome implementations, a control value can be determined 420 based onreceived 410 signals that correspond to commanded travel speed (e.g.,signals from operator inputs) and to output torque (e.g., pressuresignals from a drive circuit), but output torque may be prioritized overcommanded travel speed to determine 420 a relevant control value.Correspondingly, although adjustments based on output torque maycorrespond to a run-time displacement that is larger than would providea commanded travel speed, the larger run-time displacement that isassociated with the output torque adjustment may nonetheless becommanded, with a resulting decrease in actual travel speed relative tothe commanded travel speed. Indeed, in some implementations, control ofmotor displacement based on output torque may be implemented regardlessof any corresponding decrease (or other effect) on travel speed.

In some implementations, adjusting 430 run-time displacement can includeincreasing or decreasing run-time displacement in response to thereceived 410 signals that indicate that a particular threshold has beenexceeded. For example, run-time displacement can sometimes be increasedin response to output torque exceeding a threshold torque (e.g., asindicated by drive circuit pressure exceeding a pressure threshold). Asanother example, run-time displacement can sometimes be decreased inresponse to a commanded travel speed exceeding a speed threshold.

In some implementations, a run-time displacement can be adjusted 430based on selection of a run-time displacement (e.g., via determination420 of a corresponding control value) from within one of a plurality ofoverlapping displacement ranges. For example, a target run-timedisplacement can be selected from one of a first displacement range thatexhibits a first minimum displacement or a second displacement rangethat exhibits a second, lower minimum displacement. In some cases, firstand second displacement ranges can have a common maximum displacement.In some cases, a run-time displacement can be selected from any ofmultiple ranges, with a maximum displacement of the relevant range beingselected as a default. In some case, once a particular displacementrange has been selected, further adjustment 430 of run-time displacementmay proceed for some time using displacements that are drawn only fromthat particular displacement range.

In some implementations, control of run-time displacement of a hydraulicdrive motor for a hydraulic drive circuit may be coordinated withcontrol of run-time displacement of a hydraulic drive pump of thehydraulic drive circuit. For example, for some run-time operations, arun-time displacement of a hydraulic drive motor may be adjusted (e.g.,decreased) from an initial value only after a run-time displacement ofan associated hydraulic drive pump is increased to be at or near amaximum pump displacement. This coordinated control may help to reducesystem shocks or other adverse effects that may otherwise result asmotor displacement is decreased, particularly during a switch betweenmaximum motor displacement and maximum pump displacement.

FIG. 7 illustrates an example implementation, as part of the method 400,of coordinated control of pump and motor displacement for a run-timeoperation of a power machine. In particular, in some implementations,the method 400 includes adjusting 430 a run-time displacement for thehydraulic drive motor for a run-time operation after a run-timedisplacement of the associated hydraulic pump has been adjusted 440 tobe at or near a maximum pump displacement. (As used herein in thiscontext, “near” indicates within about 10% of maximum displacement; inother embodiments, “near” can indicate within 15%, 5%, or 2.5% ofmaximum displacement). The rate displacement change of the displacementof the hydraulic motor while the pump displacement is still changing isselected to enable a smooth transition between the pump and motordisplacement change. By a smooth transition, it is meant that the loaderwill smoothly accelerate and the change from pump displacement controlto motor displacement control will not be evident to the operator.

Correspondingly, in some implementations, run-time displacement of ahydraulic drive pump may be increased 440 from a relatively low value toa value at or near a maximum pump displacement before run-timedisplacement of a hydraulic drive motor is decreased 430 from a maximum(or other initial) displacement value. Further, for some operations,run-time displacement of a hydraulic drive motor may be initiallydecreased from an initial maximum displacement only as run-timedisplacement of the hydraulic drive pump is increased, through a rangeof hydraulic displacements near the maximum pump displacement, toapproach the maximum pump displacement.

Continuing, in some implementations, a rate of adjustment of run-timepump displacement or of run-time motor displacement can be furthercontrolled (e.g., reduced) during select portions of certain run-timeoperations. As also shown in FIG. 7, for example, a rate of increase ofrun-time pump displacement can be reduced 442 as the pump displacementis continuously increased near the maximum pump displacement. Amongother benefits as mentioned above, this controlled rate reduction mayparticularly help smooth a transition between maximum motor displacementand maximum pump displacement (e.g., during a commanded increase intravel speed for a power machine)

In this regard, FIG. 8 illustrates an example implementation of someaspects of the method 400 (see FIG. 7), during an increase in travelspeed for a power machine. Initially, at low travel speeds, motordisplacement 502 is at a maximum (e.g., as a default, as also discussedabove) and pump displacement 504 is at a minimum. Due to a commandedincrease in travel speed, the motor displacement 502 may eventually bereduced 440, corresponding to increasing travel speed for the powermachine. However, in the illustrated implementation, the motordisplacement 502 is not reduced from the initial maximum value untilafter the pump displacement 504 is first increased 440 to be near (e.g.,within 10% of) the maximum pump displacement, as indicated by referenceline 506. Additionally, to reduce potential shocks from the transitionbetween maximum motor displacement and maximum pump displacement, a rateof increase of the pump displacement 504 is reduced 442 over a range 508of displacements between reference lines 510, 512.

In the illustrated example, the range 508 of displacement over which therate of increase in the pump displacement 504 is reduced extends fromapproximately 90% of maximum pump displacement to 100% of maximum pumpdisplacement and the motor displacement 502 is initially reduced oncethe pump displacement 504 has reached approximately 90% of the maximumpump displacement. However, in other cases, reduced rates of adjustmentof pump displacement can be implemented over other ranges and reductionsin motor displacement can begin when pump displacement is otherwise neara maximum. Further, the particular rates of adjustment of thedisplacements 502, 504, the relative scale of the displacements 502,504, and the cooperative and individual relationships of thedisplacements 502, 504 to travel speed are all presented as examplesonly. A variety of other rates, scales, and relationships are possiblein other implementations. Additionally, similar adjustments according tothe general principles disclosed above may sometimes be made relative toother initial displacements or during other run-time operations,including during decreases in travel speed or for other changes inoperating states of a power machine.

In some embodiments, aspects of the invention, including computerizedimplementations of methods according to the invention, can beimplemented as a system, method, apparatus, or article of manufactureusing standard programming or engineering techniques to producesoftware, firmware, hardware, or any combination thereof to control acontrol device such as a processor device, a computer (e.g., a processordevice operatively coupled to a memory), or another electronicallyoperated controller to implement aspects detailed herein. Accordingly,for example, embodiments of the invention can be implemented as a set ofinstructions, tangibly embodied on a non-transitory computer-readablemedia, such that a processor device can implement the instructions basedupon reading the instructions from the computer-readable media. Someembodiments of the invention can include (or utilize) a control devicesuch as an automation device, a special purpose or general purposecomputer including various computer hardware, software, firmware, and soon, consistent with the discussion below.

The term “article of manufacture” as used herein is intended toencompass a computer program accessible from any computer-readabledevice, carrier (e.g., non-transitory signals), or media (e.g.,non-transitory media). For example, computer-readable media can includebut are not limited to magnetic storage devices (e.g., hard disk, floppydisk, magnetic strips, and so on), optical disks (e.g., compact disk(CD), digital versatile disk (DVD), and so on), smart cards, and flashmemory devices (e.g., card, stick, and so on). Additionally, a carrierwave can be employed to carry computer-readable electronic data such asthose used in transmitting and receiving electronic mail or in accessinga network such as the Internet or a local area network (LAN). Thoseskilled in the art will recognize that many modifications may be made tothese configurations without departing from the scope or spirit of theclaimed subject matter.

Certain operations of methods according to the invention, or of systemsexecuting those methods, may be represented schematically in the FIGs.or otherwise discussed herein. Unless otherwise specified or limited,representation in the FIGs. of particular operations in particularspatial order may not necessarily require those operations to beexecuted in a particular sequence corresponding to the particularspatial order. Correspondingly, certain operations represented in theFIGs., or otherwise disclosed herein, can be executed in differentorders than are expressly illustrated or described, as appropriate forparticular embodiments of the invention. Further, in some embodiments,certain operations can be executed in parallel, including by dedicatedparallel processing devices, or separate computing devices configured tointeroperate as part of a large system.

As used herein in the context of computer implementation, unlessotherwise specified or limited, the terms “component,” “system,”“module,” and the like are intended to encompass part or all ofcomputer-related systems that include hardware, software, a combinationof hardware and software, or software in execution. For example, acomponent may be, but is not limited to being, a processor device, aprocess being executed (or executable) by a processor device, an object,an executable, a thread of execution, a computer program, or a computer.By way of illustration, both an application running on a computer andthe computer can be a component. One or more components (or system,module, and so on) may reside within a process or thread of execution,may be localized on one computer, may be distributed between two or morecomputers or other processor devices, or may be included within anothercomponent (or system, module, and so on).

Although the present invention has been described by referring preferredembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the scope of thediscussion.

What is claimed is:
 1. A power machine having an frame, an power sourcesupported by the frame, and a power conversion system includinghydraulic drive system operably coupled to the power source andconfigured to power at least one tractive element, the hydraulic drivesystem comprising: a hydraulic circuit that includes a hydraulic pump inhydraulic communication with a hydraulic motor, the hydraulic motorbeing configured to operate with infinitely variable displacement todrive the power machine; and a control device that is configured to:determine a control value based on one or more of: a commanded travelspeed for the power machine or a pressure in the hydraulic circuit; andchanging a run-time displacement of the hydraulic motor based upon thedetermined control value.
 2. The power machine of claim 1, wherein thehydraulic motor is configured to operate selectively in a firstdisplacement range and in a second displacement range; wherein a maximumdisplacement of the first displacement range is the same as a maximumdisplacement of the second displacement range; and wherein a minimumdisplacement of the first displacement range is smaller than a minimumdisplacement of the second displacement range.
 3. The power machine ofclaim 2, wherein the control device is configured to implement, as adefault, operation of the hydraulic motor at the maximum displacement ofthe first displacement range or the second displacement range,regardless of whether the first displacement range or the seconddisplacement range is selected.
 4. The power machine of claim 1, whereinthe control device is configured to increase the run-time displacementof the hydraulic motor in response to the pressure in the hydrauliccircuit being above a given threshold.
 5. The power machine of claim 1,wherein the control device is configured to decrease the run-timedisplacement of the hydraulic motor in response to the commanded travelspeed being above a given threshold.
 6. The power machine of claim 1,wherein the control device is configured to control the run-timedisplacement of the hydraulic motor based on the commanded travel speedand the pressure in the hydraulic circuit, with the pressure in thehydraulic circuit having priority over the commanded travel speed forchanging the run-time displacement of the hydraulic motor.
 7. The powermachine of claim 1, wherein the hydraulic circuit is a hydrostatic drivecircuit.
 8. A hydraulic drive system for use in a power machine, thehydraulic drive system comprising: a hydraulic circuit that includes ahydraulic pump in hydraulic communication with a hydraulic drive motor,the hydraulic drive motor being configured to operate with infinitelyvariable displacement to drive the power machine; and a control devicethat is configured to: determine an output torque value associated withthe hydraulic drive motor; and adjust a run-time displacement of thehydraulic drive motor based upon the determined output torque value. 9.The hydraulic drive system of claim 8, wherein the control device isconfigured to adjust the run-time displacement of the hydraulic drivemotor based upon the determined output torque value, regardless ofeffect on travel speed for the power machine.
 10. The hydraulic drivesystem of claim 8, wherein the hydraulic drive motor is configured tooperate selectively in at least a first displacement range and in asecond displacement range that overlaps with, but is different from, thefirst range.
 11. The hydraulic drive system of claim 10, wherein amaximum displacement of the first displacement range is the same as amaximum displacement of the second displacement range; and wherein aminimum displacement of the first displacement range is lower than aminimum displacement of the second displacement range.
 12. The hydraulicdrive system of claim 10, wherein the control device is configured toimplement, as a default, operation of the hydraulic drive motor at amaximum displacement of the selected first or second range.
 13. Thehydraulic drive system of claim 8, wherein the control device isconfigured to increase the run-time displacement of the hydraulic drivemotor based on the determined output torque value exceeding a thresholdtorque value.
 14. The hydraulic drive system of claim 13, wherein thecontrol device is configured to determine that the output torque valueexceeds a threshold torque value based on determining that a pressure inthe hydraulic circuit exceeds a threshold pressure value.
 15. A methodof controlling run-time operation of a drive system of a power machine,the method comprising: receiving, at a control device, one or moresignals indicating one or more of a commanded travel speed for the powermachine or an output torque associated with an infinitely variabledisplacement hydraulic pump and an infinitely variable displacementhydraulic drive motor of a hydraulic drive circuit of the power machine;determining, using the control device, a control value for the hydraulicdrive motor, based on the one or more signals; and adjusting, using thecontrol device, a run-time displacement for the hydraulic drive motorbased on the control value.
 16. The method of claim 15, wherein the oneor more signals indicating the output torque include one or more signalsindicating a sensed pressure in the hydraulic drive circuit.
 17. Themethod of claim 15, wherein adjusting the run-time displacementcorresponds to a reduced travel speed of the power machine relative tothe commanded travel speed.
 18. The method of claim 15, whereinadjusting the nm-time displacement one or more of: increases therun-time displacement in response to a pressure in the hydraulic drivecircuit being above a pressure threshold; or decreases the run-timedisplacement in response to the commanded travel speed being above aspeed threshold.
 19. The method of claim 18, wherein the control valueis determined with the output torqe being prioritized over the commandedtravel speed.
 20. The method of claim 15, wherein adjusting the run-timedisplacement includes selecting a target run-time displacement fromwithin one displacement range of a plurality of overlapping displacementranges; and wherein a first displacement range and a second displacementrange of the plurality of overlapping displacement ranges have a commonmaximum displacement corresponding to a maximum possible displacementfor the hydraulic drive motor.
 21. The method of claim 15 wherein therun-time displacement for the hydraulic drive motor is adjusted based onthe control value after the control device adjusts a run-timedisplacement of the hydraulic pump to be at or near a maximum pumpdisplacement.
 22. The method of claim 21., wherein adjusting therun-time displacement for the hydraulic drive motor includes reducingthe run-time displacement of the hydraulic drive motor as the run-timedisplacement of the hydraulic pump is increased through a range ofhydraulic displacements near the maximum pump displacement to approachthe maximum pump displacement.
 23. The method of claim 22, wherein, whenthe displacement of the hydraulic pump has been increased to reach therange of hydraulic displacements near the maximum pump displacement, arate of increase of the hydraulic pump displacement is reduced.